The tribological properties of poWimide-bonded graphite fluoride films were studied wiTh a pin- on-disk friction apparatus. But instead of the conventional hemispherically tipped rider, a 440C HT stainless-steel rider with a 0.95-millimeter-diameter flat area was slid against the film. This was done so that a lighter, more closely controlled contact stress could be achieved. A 1- kilogram load was applied to this flat to give a projected contact stress of 14 megapascals (2000 psi). As for a hemispherically tipped rider under the same load, two stages of lubrication were operating. In the first stage, the film supported the load and the lubricating mechanism appeared to be the shear of a thin surface layer of the film between the rider and the hulk of the film. The second stage began after the original film was worn away, and The lubricating mechanism appeared to be the shear of very thin lubricant layers between The flat area on the rider and flat plateaus generated on the sandblasted asperities of the metallic suhstrate. The major difference between the lubricating mechanisms of The hemispherical and flat riders was That the flat wore Through the film much more slowly Than did the hemisphere. (MM)

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